In the usual cell containing monovalent silver oxide, the silver oxide is formed into a cathode, placed into a cell casing, and an electrolyte is added. A barrier or separator is positioned within the cell to separate the cathode from an anode which is also incorporated into the cell. In the completed cell the electrolyte is in contact with the cathode, anode, separator and casing. On discharge of the cell, the monovalent silver oxide in the cathode is reduced to elemental silver. The reduction of the silver oxide is believed to occur in a generally layered fashion, beginning at the interface of the cathode and separator and proceeding away from the separator.
In order to use the silver oxide cathode in a secondary cell, the layering process must be reversed during the recharging cycle. In most cases the layering process cannot be fully reversed, and this result in incomplete conversion of the silver into monovalent silver oxide. The partial reversibility of the layering process limits the capacity of the cell to accept a charge and limits the number of discharge-recharge cycles that the cell will undergo before complete exhaustion.
As a result of the inability of the layering process to be completely reversed, attempts to recharge the cell can result in an overcharge situation. During overcharge of a cell containing silver oxide, gasses such as hydrogen and oxygen form at the electrodes. These gasses cause a pressure build up in the cell which in turn causes the cell to fail.
Another factor limiting the use of monovalent silver oxide in secondary cells has been an inability to determine the state of discharge of the cell and thus the proper time to recharge the cell. The determination of the state of discharge is difficult because a cell containing monovalent silver oxide produces a flat voltage curve on discharge, and there is no apparent voltage drop until the cell is so close to complete discharge that it can not be fully recharged. The number of discharge-recharge cycles are then lower than if the cell were only partially discharged. Further, in multicelled batteries, complete discharge of any one cell before the other will result in cell reversal with possible undesirable effects such as gassing and leakage.
The inability to determine the state of discharge of the silver oxide cell has limited the use of such cells of primary batteries and to situations involving timed discharge-recharge cycles. Such timed cycles can still result in cells being discharged to the point where they cannot readily accept a recharge, since only time, not true cell capacity was measured. For this and other reasons monovalent silver oxide has not heretofore been widely used in secondary cells.